The present invention relates to a measuring head for a vacuum gauge operating according to the thermal conduction principle and including an essentially cylindrical housing and a measuring cell disposed therein so as to be sealed in a vacuum tight manner against the surrounding atmosphere and connectable with an evacuatable cavity, with a measuring filament for producing an electrical signal corresponding to the pressure in the measuring cell being disposed in the measuring cell.
A vacuum gauge of this type is disclosed in German Offenlegungsschrift [laid open patent application] No. 2,247,988 and British Pat. No. 955,661. The electrical terminals for the measuring filament are brought out of the measuring cell in an electrically insulated manner and, in the vacuum gauge according to British Pat. No. 955,661, end in the form of plug-in pins onto which suitable sockets can be plugged to connect the measuring filament with a supply and display device. Customarily, further electrical components of this device are accommodated in a Wheatstone bridge into which the measuring filament is connected. The bridge current in an unregulated thermal conduction vacuum gauge, or the bridge voltage in a regulated thermal conduction vacuum gauge, serves as a measure for the gas pressure in the measuring cell.
In the prior art vacuum gauges, the measuring filament is always disposed parallel to the longitudinal axis of the cylindrical housing so that an elongate configuration results. This configuration is desirable since it indicates right away the position in which the measuring filament is installed. This is of particular significance for the user since, due to convection phenomena within the measuring cell, the measuring signal is dependent upon the position in which the measuring filament is installed. Thus, the user must always ascertain the correct position of the measuring filament.
Measuring heads of the prior art type are not very suitable for measuring or monitoring pressures in evacuated cavities in flat components. Such components are, for example, plates or pipes having heat insulating characteristics, which are all given double walls and, in order to improve the insulating effect, are evacuated. If the relatively flat double walls of such components were equipped with the prior art measuring heads, the housings of the measuring heads would project considerably. The use of such components, in particular during transport, assembly, storage and the like, is therefore considerably impeded. Moreover, the measuring heads, and thus their proper function, are endangered by shocks. The installation of pipes equipped with measuring heads of the prior art in the ground for use as long-distance heat conduits would be possible only at considerable expense.